1. Field of the Invention
The present invention relates to a data communication apparatus which employs a data encryption technique, a control method therefor, and a program for implementing the method.
2. Description of the Related Art
Conventionally, there has been known a technique of encrypting data and transmitting the encrypted data to thereby maintain secrecy of the data. Data communication apparatuses which employ this kind of technique generally carry out encryption and decryption using a predetermined key and a predetermined encryption algorithm (encryption scheme). In most cases, the strength (security level) of the key and the encryption algorithm that can be used are fixed for the respective data communication apparatuses, or the strength of the key and the encryption algorithm that are preset in the data communication apparatuses are used (for example, refer to Japanese Laid-Open Patent Publication (Kokai) No. H07-162693).
With such a conventional technique, therefore, time required for encryption of data increases as the size of data to be transmitted increases. During the data encryption process, processing of other functions are restricted, thus causing unfavorable effects on operation of other functions.
As measures to avoid such a problem, it can be envisaged that the encryption algorithm is automatically changed to a more simplified one, or the key strength is lowered, according to the size of data to be transmitted. However, in these cases, a problem arises that the data is transmitted by a key strength or an encryption algorithm which is not intended by the user.